The present invention relates generally to expansible plugs.
More particularly, it relates to an expansible plug which has expansible tongs over an expansible region and expandable by a screw.
Accordingly, it is an object of the present invention to provide an expansible plug of the above mentioned general type, which avoids the disadvantages of the prior art.
More particularly it is an object of present invention to develop an expansible plug of the type mentioned so that its anchoring strength in the drilled hole is increased.
In keeping with these objects and with others which will become apparent hereinafter, one feature of present invention resides, briefly stated, in an expansible plug which has expansible tongs extending over an expansible region and expandable by screwing a screw, wherein in accordance with the present invention, the expansible plug is oversized in the expansible region.
The expansible plug according to the invention has, in the region of its expansible tongues, a greater transverse dimension that the drilled hole in which it is to be anchored. On insertion of the expansible plug into the drilled hole, the expansible tongues are pressed radially toward one another with the result that spaces between the expansible tongues narrow or close. That yields large-area contact of the expansible plug against the entire, or at least virtually the entire circumferential surface of the wall of the drilled hole. The contact surface, which is increased in comparison with that of known expansible plugs, improves the hold of the expansible plug according to the invention in the drilled hole and increases its anchoring strength.
In accordance with the present invention the spaces between the expansible tongues are preferably of such dimensions that they close completely or virtually completely at least at the circumference of the expansible plug when the expansible plug is inserted into the drilled hole. As a result, in the expansible region of the expansible plug, a substantially closed circumferential surface is obtained without interruptions between the expansible tongues and thus the largest possible contact surface against the wall of the drilled hole for a given diameter of the drilled hole.
In accordance with a preferred embodiment of the invention, the expansible plug has two expansible tongues, arranged opposite to and spaced from one another, that are, in cross-section, substantially in the shape of a segment of a circle. Between those two expansible tongues there are arranged two further expansible tongues that are slightly spaced from one another at a central portion of the expansible plug and extend radially as far as the outer circumference. The expansible plug has in the region of its expansible tongues a cylindrical surface that is interrupted at the space between expansible tongues. The diameter of this surface is greater than the diameter of the drilled hole into which the expansible plug is to be placed. That arrangement of the expansible plug makes it possible for the expansible tongues to be compressed radially on insertion into the drilled hole in such a manner that the interruptions in the surface close.
In accordance with a further development of the invention, the expansible tongues that are provided between the expansible tongues of circle segment-shaped cross-section are of U-shaped cross-section. A yoke-like wall is provided at the circumference of the expansible plug and rounded to match the diameter of the drilled hole. Leg-like walls of the expansible tongues of U-shaped cross-section run into the inside of the plug. Their free ends are spaced from one another and form a longitudinal guide for the screw to be screwed in. In addition to the good longitudinal guidance of the screw, that construction of the invention has the advantage that the two expansible legs of U-shaped cross-section are pressed away from one another radially by the screw that is screwed in. At the same time, the leg-like walls of those expansible tongues are expanded away from one another radially, at right angles to the direction in which those two expansible tongues are pressed away from one another. As a result, the leg-like walls press away from one another the other two expansible tongues of circle segment-shaped cross-section, likewise, radially relative to the expansible plug and at right angles to the expansible tongues of U-shaped cross-section. The radial expansion of all four expansible tongues produces effective contact in the drilled hole, which yields a high anchoring strength. The torque for screwing in the screw into the expansible plug according to the invention is converted highly efficiently into expansion of the expansible plug.
Preferably, the expansible plug according to the invention has three, especially four or more, expansible tongues. Therefore the expansible plug""s does not have a preferred direction. For example, there are no only two expansible tongues capable of taking up greater transverse forces at right angles to a plane lying between its two expansible tongues, that is to say in the direction in which its expansible tongues are expanded away from one another, than in the said plane. A further advantage of the greater number of expansible tongues is the better distribution of the expansion forces over the entire circumference of the drilled hole in which the expansible plug is anchored. That increases the anchoring strength of the expansible plug in the drilled hole. A further advantage is that the more uniform impingement upon the wall of the drilled hole reduces locally high loadings on the wall of the drilled hole and therefore a local collapse of the wall of the drilled hole is avoided, which can result from local deformation or destruction of the masonry in which the drilled hole has been made. That improves the anchoring of the expansible plug especially in soft or porous masonry.
In accordance with a further feature of the present invention, a uniform impingement upon the wall of the drilled hole around its entire circumference is enhanced when in accordance with the present invention the expansible tongues have the cross-sectional area with approximately the same area. Such identically sized cross-sectional areas of the expansible tongues bring about an approximately identically great deformation of the expansible tongues, which, as the expansible plug is expanded, are squeezed between the screw which is expanding them away from one another and the wall of the drilled hole. The approximately identically great deformation results in approximately identical great contact pressure forces of the expansible tongues against the wall of the drilled hole.
The anchoring of the expansible plug in the drilled hole is improved when in the invention at least one of the expansible tongues has one wing element, especially two wing elements opposite to one another and projecting in an approximately tangential direction or in an approximately circumferential direction. Such wing elements increase the resilience of the expansible tongues and bring about an increase in the contact surface.
In accordance with one embodiment of the invention, expansible tongues are provided that are of approximately circle segment-shaped cross-section. That has the advantage that all the expansible tongues can be constructed having the same cross-section. Thereby all the expansible tongues have the same expansion forces.
In another embodiment, the expansible tongues are connected to one another at both ends. That improves a torsion rigidity of the expansible plug and prevents the expansible plug from twisting about its longitudinal axis as the screw is screwed in. It also avoids a situation where one or more expansible tongues is/are pressed aside tangentially in the drilled hole by the screw. As a result, the screw and expansible tongue take up positions adjacent to one another.
In order to guide the screw reliably between the expansible tongues in the longitudinal direction of the expansible plug, in the invention the expansible tongues are constructed having guide grooves that run in the longitudinal direction on their inside sides that face one another. The bordering edges of the guide grooves guide the screw.
The spaces between the expansible tongues preferably form slits in planes that are parallel with one another. The slits can be formed in the injection-moulding by ribs that project parallel with one another into a hollow area of a mould. As a result, the finished expansible plug can be removed without difficulty from an injection moulding die. The expansible plug according to the invention can, as a result, be manufactured using a simple injection moulding die having two corresponding die halves that are arranged in mirror-image having substantially semi-cylindrical recesses into which there extend the ribs for forming the slits between the expansible tongues of the expansible plug, and also a core. In order to facilitate the removal of the expansible plug from the injection moulding die, the slits may broaden out towards the circumference of the expansible plug.
In accordance with a further embodiment of the present invention, the expansible tongues of the expansible plug may be separated from one another over their entire length and may be connected to one another only at one end or at both ends. In that construction of the invention, the expansible tongues can be expanded apart with minimal force, as a result of which the torque for screwing-in the screw is small. In a different construction of the invention, expansible tongues that are adjacent to one another are connected to one another resiliently at individual points along their length or continuously. In that construction of the invention, the longitudinal guidance of the screw to be screwed in is improved.
The novel features which are considered as characteristic for the present invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.